As electronic equipment becomes further miniaturized and multifunctional, higher density has been requested also for the circuit boards used in the electronic equipment. For making the density of the circuit boards higher, the circuit boards are generally multilayered. The multilayer circuit board is typically obtained by laminating an electrical insulating layer on the surface of an inner layer board on which conductor circuits (conductor patterns) are formed on the outermost surface thereof and forming a conductor circuit on the electrical insulating layer, and it is also possible to further laminate a number of electrical insulating layers and conductor circuits as necessary. Multilayer circuit boards such as multilayer printed wiring boards typically have three or more “conductor patterns/electrical insulating layers”, and there are known those with more than 70 layers among them.
In the multilayer circuit boards, adhesion between the electrical insulating layers and the conductor patterns (circuits) formed thereon (hereinafter abbreviated as “pattern adhesion”) has become important in order to enhance durability and ensure long life. Generally, the electrical insulation layers to make multilayers are formed using electrical insulating resins.
As the method for enhancing the pattern adhesion, a method in which the surface of the electrical insulating layer is roughened and then conductor patterns are formed thereon is widely adopted, as disclosed in Japanese Patent Laid-Open No. 11-23649, Japanese Patent Laid-Open No. 11-286562, and Japanese Patent No. 2877110. In order to further improve the pattern adhesion, a method for coating adhesives for electroless plating containing polymer components such as rubber or resins on the roughened electrical insulating layers (Japanese Patent Laid-Open No. 2001-192844, Japanese Patent Laid-Open No. 2001-123137, and Japanese Patent Laid-Open No. 11-4069) is proposed.
However, some treatment after forming the electrical insulating layers cannot provide sufficient pattern adhesion for a long period of time when temperature or humidity changes, and causes delamination to shorten the life of the circuit boards.
Japanese Patent Laid-Open No. 2001-160689 proposes a method in which the adhesion between an inner layer board and an electrical insulating layer formed thereon is improved by laminating a thiol compound layer on the inner layer board comprising an electrical insulating layer and a conductor circuit formed thereon so as to cover the conductor circuit, and by forming thereon an electrical insulating layer containing an cycloaliphatic olefin polymer.
According to the method disclosed in Japanese Patent Laid-Open No. 2001-160689, the adhesion between the inner layer board and the electrical insulating layer formed thereon can be improved and the delamination can be suppressed, but the adhesion at the interface between the electrical insulating layer and the conductor circuit formed thereon is insufficient.
Therefore, in multilayer circuit boards, the development of new technology is required for improving the adhesion at the interface between an electrical insulating layer formed on an inner layer board to make multilayers and a conductor circuit formed on the electrical insulating layer.
On the other hand, the members comprised of resin base materials with metallic microlines (metallic patterns or conductor patterns) formed on the surface are used for semiconductor devices, semiconductor device mounting components, various panel displays, IC cards, optical devices and the like.
Typically, these metallic patterns are formed by plating. The methods for forming metallic patterns by plating include (1) a method for forming a metallic pattern by applying electroless plating on the whole surface of a resin base material, forming a resist pattern thereon using a plating resist, growing a metallic layer by electrolytic plating via the resist pattern, and removing an unnecessary electroless plating part by etching (semi-additive process), and (2) a method for plating a desired pattern by electroless plating on a resin base material to form a metallic pattern and growing an electroplated metal thereon as necessary (fully-additive process).
The latter method using a pattern plating process is excellent in productivity, in that metal corrosion by the chemicals used for removing the unnecessary electroless plating part does not occur and a step for removing the electroless plating is not required.
In the pattern plating, metallic patterns can be easily obtained by forming an initiator pattern (also referred to as an electroless plating film) comprised of a plating-inducing substance on the surface of the resin base material and plating on this pattern (e.g., Japanese Patent Laid-Open No. 7-263841). A large number of investigations have been carried out on the plating-inducing substances for the purpose of improving the adhesion to resin base materials and pattern shapes. The plating-inducing substances which are proposed include a conductive material comprised of a mixture of a conductive polymer or a precursor thereof with water or a polar solvent (Japanese Patent Laid-Open No. 2002-26014), a composition consisting of a soluble palladium salt, a water-soluble solvent and water (Japanese Patent Laid-Open No. 7-131135 and Japanese Patent Laid-Open No. 7-245467), and a material containing a photosensitive palladium polymer chelate compound (Japanese Patent Laid-Open No. 2000-147762).
Further, Japanese Patent Laid-Open No. 11-350149 includes resin compositions such as (1) a low molecular weight compound having an N—H bond, an adhesive polymer having a C═C double bond, and a polybasic acid having a C═C double bond, (2) an adhesive polymer having a high N—H bond density, and a low molecular weight polybasic acid or a monobasic acid having a C═C double bond compatible therewith, (3) a resin component forming an N—H bond in a curing reaction and a polybasic acid having a C═C double bond, and (4) a resin component forming an N—H bond in a curing reaction and an adhesive polymer having a C═C double bond on a main chain and a polybasic acid having a C═C double bond.
These plating-inducing substances can ensure easy formation of metallic patterns on resin base materials. However, in the actual use of the resin base materials, the improvement of the adhesion between metallic patterns and resin base materials has been important problems.
In order to improve the adhesion, the surface of the resin base materials is generally roughened by a physical or chemical method so as to obtain a surface roughness Ra of several μm. However, roughness of the surface by roughening reduces the accuracy of metallic patterns, and may cause noise in electrical signals in the case of circuit boards.
Therefore, there is desired the development of a method for obtaining high adhesion between resin base materials and metallic patterns without roughening the surface of the resin base materials.